Telephony has been rapidly changing in recent years. With the development and growth of the Internet and other packet-based network types, communications carriers have been developing networks that either extend from the public switched telephone network (PSTN) or operate independent from the PSTN.
Remotely accessed telecommunications systems, such as voicemail, interactive voice response (IVR) systems, and interactive keypad response systems, generally use DTMF signals to enable a user to interact these systems. The remotely accessed telecommunications systems generally operate by recognizing and responding to DTMF signals having amplitudes with a certain power level range.
As new packet-based networks have been developing, additional equipment has been developed to interface telephones to the networks and the networks with each other. In addition, the packet networks tend to be smaller, which results in more network-to-network interfaces (NNI) being used.
As understood in the art, communications signals naturally attenuate when communicated through devices and over transmission lines. The amount of attenuation of communications signals is generally known for different types of network devices and networks. It is further known that attenuation results from an digital-to-analog (D/A) process at different end-point network adapters and converters. For example, an integrated access device, which is a customer premises device that provides access wide area network and the Internet, aggregates multiple channels of information, including voice and data, across a single shared link to a carrier or service provider uses D/A converts to convert DTMF signals being communicated in data packets into analog DTMF signals.
FIG. 1 is an illustration of an exemplary network 100 composed of a PSTN 102, voice over broadband (VoBB) IP networks 104a-104c (collectively 104), and voice over Internet protocol (VoIP) peering network 106. Communications may be performed between the PSTN 102 and VoBB IP network 104 via media gateways 108a-108c (collectively 108). Communications between each of the sub-networks 104 and 106 are performed via session border controllers 110a-110c (collectively 110). As shown, communications between telephones may pass through the PSTN network 102 or avoid the PSTN network 102 by being routed directly to packet networks 104 and 106. Four exemplary call paths are shown in FIG. 1, including calls paths 1, 2, 3, and 4.
Call path 1 is a traditional call path that is established between a first telephone 112 that communicates via an access network 114 from the telephone 112 via a class 5 switch 116. The class 5 switch 116 routes the call via the PSTN network 102 to class 5 switch 118 via access network 119 to a receiving telephone 120. Call path 1 is considered a conventional call over the PSTN network 102 on plain old telephone (POTS) networks.
Call path 2 is shown to traverse via the access network 114, class 5 switch 116, and PSTN network 102. Call path 2 further is established over media gateway 108b to the VoBB IP network 104b via the Internet access device (IAD) 122 to telephone 124. Call path 3 is routed from the telephone 112 via the access network 114 and class 5 switch 116 to a border control switch (BCS) 126 to communicate via the VoIP peering network 106. From the VoIP peering network 106, the call path continues through session border controller 110b to the VoBB IP network 104b and via the IAD 122 to telephone 124.
In the case where a packet-based telephone 128 places a call to another packet-based telephone 124, call path 4, which passes through IAD 130 to VoBB IP network 104a. From the VoBB IP network 104a, call path 4 continues through SBC 110a, VoIP peering network 106, SBC 110b, VoBB IP network 104b, and IAD 122 to telephone 124.
With the traditional call path 1, each element over which the call path 1 is established has a known attenuation value. If a minimum low frequency component level starts at −10 dBm (low current=long loop), add about 7 dB loss (i.e., −7 dB) for each of 2 long loops, and include a 6 dB receive loss pad in the far end CO, the low frequency component power level is computed as −10−2×7−6=−30 dBm The corresponding calculation for the high frequency component starts with a level of −8 dBm and includes an additional −4 dB twist for each loop, so the high frequency component power level is computed as −8−2×7−2×4−6=−36 dBm. For example, at the telephone 112, the low frequency DTMF component level is −10 dBm, access network 114 may have an attenuation of 7 dB, assuming no attenuation through class 5 switch 116, far end class 5 switch 118 has an attenuation (receive loss pad) of 6 dB, and access network 119 has an attenuation of 7 dB. In total, the attenuation of call path 1 is 20 dB for low frequency DTMF signal (i.e., a power level that is −20 dB below the DTMF signal power generated by the telephone). Therefore, the low frequency DTMF component power level at the far end telephone system may be −30 dBm.
The far end telephone system needs to recognize this low power level (−30 dBm), low frequency DTMF component for making an appropriate response. For the same path, the attenuation for the high frequency DTMF component of signal level −8 dBm turns out to be 28 dB (−2×7−2×4−6=−28 dB) including an additional −4 dB twist for each loop (i.e., the far end telephone system needs to recognize this low level (−8 dBm−28 dB=−36 dBm), high frequency DTMF component power level for making an appropriate response). It is to be noted that in traditional network the levels of minimum low and high frequency DTMF signals received at the CO are −17 dBm and −19 dBm respectively with an attenuation of maximum −7 dB and −1 dB respectively. A DTMF signal that is attenuated by 20 dB to 28 dB may cause the remotely accessed telecommunications system to not receive DTMF signal inputs from the telephone to the remotely accessed telecommunications system properly. The other call paths, call paths 2, 3, and 4, pass over media gateways, broadband networks, IP networks, border control switches, Internet access devices, session border controllers, etc. Each of these network components have a range of attenuation that results from a signal passing through the respective network devices. For example, in addition to the amount of attenuation as stated above the broadband networks (e.g., VoBB IP network 104a) has an attenuation of 5 dB, central office (not shown) has an attenuation of 6 dB, media gateways have an attenuation of 6 dB, and integrated access devices have an attenuation of 6 dB. Each of these attenuations is a minimum value and the attenuation may have additional attenuation of a few dB. Because communications over multiple packet networks may occur, attenuation that is higher than conventional calls being placed over the PSTN network 102 may result. For example, if a telephone call is placed from a telephone and passes over multiple packet networks, such as call path 3, then attenuation resulting from the call being placed over multiple devices and multiple packet networks cause signals communicated over the call path to be attenuated by the sum of each of the attenuations of the network devices and networks over which the call path traverses. It is not uncommon that an attenuation of 30 dB or higher (i.e., −30 dB below the initial signal) occurs when a communication path crosses multiple packet networks.
As a result of higher attenuation occurring when a telephone call is placed from a conventional telephone via the PSTN network 102 to telephones operating on packet networks, operation of DTMF signals may be affected due to the attenuation of the high and low frequencies of the DTMF signals being attenuated below operational standards of remotely accessed telecommunications systems. For example, if a remotely accessed telecommunications system expects to receive DTMF signals with a minimum power level or amplitude of −38 dBm, a signal that is attenuated by 28 dB or higher may cause the remotely accessed telecommunications system to not receive DTMF signal inputs from the telephone to the remotely accessed telecommunications system properly. As more and more packet networks are established and integrated for use by telecommunications, higher levels of attenuation currently cause and are expected to cause more problems for users of telephones attempting to access remotely accessed telecommunications systems. For example, if a caller from India were to call a voicemail system in the United States, the voicemail system may be incapable of responding to DTMF signals from the caller in India due to the DTMF signals being attenuated to the point that the voicemail system cannot determine the DTMF signals being entered by a user pressing buttons on his or her telephone in India. What is needed is a way for DTMF signals traversing packet networks and network devices enable users to interface with remotely accessed telecommunications systems.